167 
of Opal, Wood-stone and Diamond. 
not the gritty feel of those that contain silica, are uncommonly 
hard, dark-coloured, and take a high polish ; these I conjec- 
ture, may be somewhat of an adamantine nature. If this should 
prove to be the case, it would neither be surprising nor unex- 
pected, that such trees may secrete carbon in the adamantine 
state, which, on being removed from the influence of the living- 
principle of the plant, would, by the power of affinity., form 
into true diamonds, — just as the silica secreted from the bam- 
boo takes the form of opal, and that from teak wood the charac- 
ters of hornstone. 
The preceding statement, then, seems to give plausibility to 
the idea, that some sorts of trees may be characterised by the 
power of forming a mineral matter of the nature of hornstone ; 
that others secrete silica, which assumes the character of opal ; 
while others may possess the power of secreting and forming 
diamond. 
It may be added, that the carbonate of lime, which occurs 
in all the rock formations, from the primitive granite to the new- 
est alluvial formation, is one of the mineral substances secreted 
by vegetables. Some lichens and the chara tribe afford re- 
markable examples of this fact. 
Art. XVIII. — An Account of some Electro-Magnetic Experi- 
ments made in the University of Utrecht. By Dr Van Beek, 
Major-General Baron Van Zuylen, Van Nyevelt, and 
Professor G. Moll. Communicated by the Authors. 
It was stated some time ago, by Professor Seebeck, in some of 
the French and German scientific journals, that Antimony , 
brought into proper contact with another metal, and unequally 
heated, would cause the magnetic needle to deviate from its 
meridian. With a view to ascertain this fact, and to investigate 
whether this property was restricted to antimony, or extended 
to other metals, the following experiments were made. 
1. A parallelopiped of Antimony was procured, about fifteen 
inches long, and one inch square. This bar was prepared by 
treating crude antimony with sulphate of potash and tartrate of 
potash. A slip of copper was attached to both ends of the anti- 
